This invention relates to a barrier ribs material for a plasma display panel (hereinafter may simply be called a xe2x80x9cPDPxe2x80x9d).
A plasma display is a self-emission flat display and has excellent characteristics such as a light weight, a reduced thickness, and a wide viewing angle. In the plasma display, a display screen can easily be widened. Therefore, the plasma display attracts attention as one of the most promising display devices.
FIG. 1 is a sectional view showing a typical structure of a PDP of the plasma display. The PDP illustrated in FIG. 1 comprises a front glass substrate 1, a rear glass substrate 2 faced to the front glass substrate 1, and a plurality of barrier ribs 3 for dividing a cavity between the front and the rear glass substrates 1 and 2 into a number of gas discharging sections. In the FIGURE, only one gas discharging section is shown. On the front glass substrate 1, a pair of transparent electrodes 4 are formed.
On the transparent electrodes 4, a dielectric layer 5 is formed to cover an entire surface of the front glass substrate 1. In order to stably generate a plasma, the dielectric layer 5 is covered with a protection layer 6 of MgO.
On the rear glass substrate 2, a data electrode 7 is formed between the barrier ribs 3. A phosphor 8 is applied to cover the data electrode 7.
When an electric voltage is applied between the transparent electrodes 4, the plasma is generated in the gas discharging section. Ultraviolet radiation is generated by the plasma and irradiated onto the phosphor 8. The phosphor 8 is excited by the plasma to emit light.
In the PDP illustrated in FIG. 1, the barrier ribs 3 are formed on the rear glass substrate 2. The front glass substrate 1 is faced to the rear glass substrate 2 through the barrier ribs 3. Then, the front and the rear glass substrates 1 and 2 are attached to each other. In this manner, the PDP is formed.
In the PDP illustrated in FIG. 1, the barrier ribs 3 are formed directly on the rear glass substrate 2. In another known PDP, a dielectric layer for electrode protection is formed on the rear glass substrate 2 to cover the data electrode 7 and the barrier ribs are thereafter formed on the dielectric layer.
In order to form the barrier ribs 3, use may be made of a multilayer printing process or a sandblasting process. In the multilayer printing process, screen printing is repeatedly carried out a plurality of number of times at positions where the barrier ribs are to be formed. Thus, a multilayer structure is formed by repeatedly applying a barrier ribs material to thereby form the barrier ribs.
The sandblasting process is carried out in the following manner. On the entire surface of the rear glass substrate, directly or through the dielectric layer, a paste of the barrier ribs material is applied by screen printing and then dried, or alternatively, a green sheet of the barrier ribs material is put. Thus, a barrier rib layer of a predetermined thickness is formed. At predetermined positions on the barrier rib layer, a photosensitive resist is applied to produce a resist film through exposure and development. Thereafter, an area without the resist film is removed by sandblasting to form the barrier ribs at the predetermined positions.
Generally, the barrier ribs material is required to allow firing at a temperature not higher than 600xc2x0 C. in order to prevent deformation of the glass substrate, to have a coefficient of thermal expansion of 60xc3x97 to 85xc3x9710xe2x88x927/xc2x0C. (30 to 300xc2x0 C.) equivalent to that of the glass substrate in order to prevent cracking or separation of the barrier ribs, and to have resistance against an alkali solution used upon forming the barrier ribs.
As the barrier ribs material satisfying the above-mentioned demands, use is generally made of a mixture of glass powder and filler powder. As the glass powder, a low-melting-point glass is used. Generally, a PbO-based glass is widely used. As the filler powder, alumina powder is widely used so as to retain the shape of the barrier ribs and to obtain sufficient strength.
In the meanwhile, the PDP is disadvantageous in that power consumption is high because the phosphor is irradiated with the ultraviolet radiation to emit light. In view of the above, consideration is made of reduction in power consumption. In order to reduce the power consumption, it would be effective to lower the dielectric constant of the barrier ribs. To this end, it is proposed to form the barrier ribs of a porous structure or to use the filler powder having a low dielectric constant as the barrier ribs material.
However, if the barrier ribs have a porous structure, an influence of a gas passing through the barrier ribs may cause degradation in brightness or defective lighting. Furthermore, the strength of the barrier ribs is degraded to cause the barrier ribs to be broken off.
As the filler powder having a low dielectric constant, there is known a silica-based filler such as xcex1-quartz powder or fused silica powder. However, these materials are lower in mechanical strength than alumina. It is therefore difficult to form the barrier ribs having sufficient strength.
It is therefore an object of this invention to provide a PDP barrier ribs material capable of forming a barrier rib having a low dielectric constant and a high mechanical strength.
As a result of extensive studies, the present inventors have found that the above-mentioned object is achieved by the use of a spherical silica-based filler as filler powder and hereby propose this invention.
According to one aspect of this invention, there is provided a PDP barrier ribs material comprising glass powder and silica-based filler powder, the silica-based filler powder comprising fused silica powder and xcex1-quartz powder, at least a part of the silica-based filler powder being spherical filler powder.
The remaining part of the silica-based filler powder may be aspherical filler powder.
The ratio of the spherical filler powder and the aspherical filler powder may be 30:70 to 100:0 in mass ratio.
The aspherical filler powder may have a 50% average particle size between 0.5 to 3 xcexcm.
The spherical filler powder may have a 50% average particle size between 2 and 8 xcexcm.
The fused silica powder may be spherical and form the spherical filler powder.
On the other hand, the xcex1-quartz powder may be aspherical.
The ratio of the fused silica powder and the xcex1-quartz powder may be 20:80 to 90:10 in mass ratio.
The ratio of the glass powder and the silica-based filler powder may be 70:30 to 95:5 in mass ratio.
The ratio of the spherical fused silica powder and the aspherical xcex1-quartz powder may be 30:70 to 90:10 in mass ratio.
According to another aspect of this invention, there is provided a PDP barrier ribs material comprising glass powder and silica-based filler powder in mass ratio of 70:30 to 95:5, the silica-based filler powder comprising spherical fused silica powder having a 50% average particle size of 2 to 8 xcexcm and aspherical xcex1-quartz powder having a 50% average particle size of 0.5 to 3 xcexcm, the ratio of the fused silica powder and the xcex1-quartz powder being 30:70 to 90:10 in mass ratio.
Throughout the description and the claims, a xe2x80x9csphericalxe2x80x9d shape is not restricted to a true sphere but is defined as an object having a predetermined width and exhibiting the effect of this invention. Therefore, any shape similar to the sphere is contained also. Specifically, the xe2x80x9csphericalxe2x80x9d shape is defined as a three-dimensional object formed by a smooth surface at a predetermined uniform distance from the center of spherical shape, allowing a variation of xc2x125%, preferably, xc2x115%. Such spherical powder can be obtained, for example, by spraying material powder into a flame.